Control system for stacking equipment

ABSTRACT

A NOVEL BED BLENDING SYSTEM IS DISCLOSED WHICH PRODUCES UNIFORM THICKNESS LAYERS IN THE BED. A CONVEYOR FEEDS A CONVENTIONAL TRAVELING STACKING BOOM WHICH DEPOSITS MATERIAL ON THE BED AS IT TRAVELS. THE BED IS FORMED, LAYER BY LAYER, ON SUCCESSIVE PASSES OF THE STACKER. THE CONTROL SYSTEM MONITORS THE FEED RATE AND CONTROLS THE STACKER SPEED TO PROVIDE FOR CONTROLLED LAYER THICKNESS IN THE BED AS CONVEYOR SPEED AND MASS FEED VARY. THE CONTROL SYSTEM IS SO DESIGNED THAT A LAYER OF THE BED IS UNIFORM ALONG THE BED BUT IS CAPABLE OF PROVIDING VARIATIONS IN BED LAYER THICKNESS FROM ONE LAYER TO THE NEXT.

Sept. 21,, 1971 s. c'. MAYER 1 5 3 CONTROL SYSTEM FOR sucxmc mumu'an'rFiled Nov. 24, 1969 gsheets-sheet 1 INVENTOR. erald C. Mayer agan Sept.21, 1971 e. c. MAYER CONTROL SYSTEM FOR STACKING EQUIBIENT 2Sheets-Sheet 2 Filed Nov. 24; 1969 INVENTOR.

W M W& m .M a? M y QB United States Patent Office Int. Cl. B65g 57/00US. Cl.' 214-10 4 Claims ABSTRACT OF THE DISCLOSURE A novel bed blendingsystem is disclosed which produces uniform thickness layers in the bed.A conveyor feeds a conventional traveling stacking boom which depositsmaterial on the bed as it travels. The bed is formed, layer by layer, onsuccessive passes of the stacker. The control system monitors the feedrate and controls the stacker speed to provide for controlled layerthickness in the bed as conveyor speed and mass feed vary. The controlsystem is so designed that a layer of the bed is uniform along the bedbut is capable of providing variations in bed layer thickness from onelayer to the next.

BACKGROUND This invention relates to an improvement in bed blendingsystems. Systems of this type have been in use for some sixty years allover the world. U. S. Pat. No. 677,677 issued July 2, 1901 to Messiteris an example of the early systems.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a plan view of the layout of a modern bed blending system;

FIG. 2 is an elevation view of the system illustrated in FIG. 1;

FIG. 3 is a plan view of an early bed blending system;

FIG. 4 is an elevation view of the system illustrated in FIG. 3;

FIG. 5 is a cross section of FIG. 4;

FIG. 6 illustrates the stacker conveyor; and

FIG. 7 is a schematic diagram of the control system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Today, bed blending is used fora variety of purposes. In one application, it can be used to average outraw ore taken from a mine so as to obviate the necessity for expensiveand wasteful selective mining. In another type of use, a bed blendingsystem can be used to mix a plurality of ingredients to a particularrecipe in preparation for further processing. Such a recipe allows theprocessing plant to be operated for efi'icient processing with a minimumof maintenance and adjustment. This also allows use of highly efli cientand, if desired, automated processing plants with further savings incosts.

The Messiter patent, mentioned above, provides a good showing of thetheory behind bed blending which will now be explained. FIGS. 3, 4 and5, reproduced from Messiter, show respectively plan, elevation and crosssection views of a bed blending system. The material, such as iron ore,coal, cement, etc., is fed into the system on conveyor b. FIGS. 3, 4,and 5 show diagrammatically how the material travels down the conveyorto the tripper device a and is laid onto the pile f. The continous backand forth travel of the tripper device results in a plurality of layersbeing formed. FIG. shows that as the material is deposited, a roughlytriangular pile is formed. As the pile grows, the material is depositedat the apex and falls down both sides of the pile. If now the pile issliced transversely of its length, an accurate sample of all thematerial 3,606,954 Patented Sept. 21, 1971 in the pile is obtained. Thatis, the slice represents a weighted average of that which went into thepile. Although perfect blending is not usually achieved, a Wellengineered system will approach this figure, within commercialtolerances. The remaining element of the system provides a device whichperforms the slicing operation to reclaim the desired result. TheMessiter patent employs plow-like blades, g, connected to a chain tocontinuously slice the pile at its base. As the resulting product isreclaimed, the plow-chain combination moves down the bed. The resultingmix, which is now blended so that particle size and chemical analysisare uniform, is carried out on conveyor k.

A modern bed blending system is shown in FIGS. 1 and 2.. A plurality ofbeds 1 are shown. Raw material is brought in by distributing conveyor 2.The material can then be switched to one of the stacking and reclaimingconveyors 3, 4, or 5 from distributing conveyors 2, 6, or 7. Theillustration shows the incoming material on stacking conveyor 4.Tripping trailers 8 and 9 are provided for discharging material fromconveyor 4 onto the stacker conveyors 19. As illustrated, trailer 8 isnot in use and trailer 9 is operatively associated with the stacker 11.The stackeris capable of feeding one or both piles directly adjacent itspath. As stacker 11 moves back and forth along the bed, the materialejected forms the piles 1. Once the bed is built up and it is determinedto be ready for reclaiming, the reclaimer 12 is put into operation. Thereclaimer 12 may be of the bucket wheel type shown, for example, inDischinger, US. Pat. 3,069,027, issued Dec. 18, 1962. As explained inthat patent, the reclaimer continuously slices the pile and carries offthe resulting blended product. FIG. 1 illustrates reclaiming conveyor 3carrying off the blend to collecting conveyor 13 for subsequent use.

As can be seen, the theoretical basis of bed blending depends on thetransverse slice accurately portraying, in physical size and chemicalcontent, the material comprising the entire bed. Since the veryobjective of these systems is to blend materials, one begins with atleast two different materials to be blended. Each is, in turn, fed tothe stacker and laid on the bed. In order for each transverse slice tobe an accurate cross section of the material in the entire bed, rigidcontrol must be exercised to ensure that the layers do not varylongitudinally. The three variables that control layer thickness are (a)belt loading, that is the density of material on the conveyor; (b) beltspeed; and (c) stacker speed. The product of belt loading and belt speedis mass flow, which, when divided by stacker speed results in density inthe bed. Since the area of the bed is fixed, this is directlproportional to the layer thickness. And, in fact, the prior art doesshow attempts at control of these factors. The only prior alternativewas manual control of both stacker speed and belt speed. In the presentinvention, a bed blending system is disclosed which is capable of copingwith situations in which the belt loading is variable and notsusceptible to control. Furthermore, applicant has recognized that theonly requirement for effective blending is unvarying layer thicknessalong the length of the bed and that, in fact, variations of layerthickness from one layer to the next are not only immaterial but suchvariations may serve to obviate still another problem.

This problem relates to non-integral numbers of layers. I

in most cases is within acceptable commercial tolerances.

However, when blending to a recipe, which may call for the equivalent of3 layers, a problem is present which the prior art could not cope with.Discarding the non-integral portion will throw off the recipe by 14%.

Using the material as /2 layer will result in a 33 /2% I variation inslices. Either variation is too great to be 7 commercially acceptable.The control system of the present invention solves this problem byassuring longitudinal uniformity, yet providing for variations in layerthickness between layers. In the example given above, the excess /2layer would be spread out over the entire bed at /2 normal thickness.This will provide the proper recipe and proper blending.

Another advantage of the present invention is the fact that the controlsystem readily lends itself to remote operation which, in turn, iscapable of automation if desired.

FIG. 6 shows the stacker 11 used in the present invention. The stacker11 travels on rails 14. A conventional frame 15 supports the operatingelements on wheels 16. Preferably each wheel 16 is driven by a separateAC. motor, however, only one motor 16 is shown in FIG. 7 for the sake ofclarity. The stacker trailer 9 supports a conveyor 4 so as to dischargeontostacker conveyors 19 mounted on boom arms 20. Boom arms 20 may beraised or lowered by conventional cable haulage systems 21 so as toclear the top of the bed as the bed increases in height. It should berecognized that conventional stackers can often have only one arm whichpivots about a vertical axis so as to serve beds on either side of thestacker. Likewise, an automatic stacker can be made in the form shown inFIGS. 3 through 5 wherein material is simply discharged onto thestockpile by a conveyor which extends over the center of the pile andwherein the conveyor is provided with a powered tripper for dischargingmaterial from the conveyor and which tripper is adapted to move back andforth between the ends of the pile. Thus, for the purpose of thisinvention, it is immaterial what type of stacker is employed. Regardlessof the type of stacker that is employed, this invention requires thatthe Weight of the material being discharged therefrom be monitored by ascale such as indicated by reference numeral 22. Thus, scale unit 22 isshown on both boomsof stacker 11 as well as also being indicated in thevicinity of the discharge point of the stacker shown in FIG. 4. For thesystems shown in FIGS. 1, 2, 6 and 7, the scales 22! are mounted nearthe outer edge of the booms 20 and measure the material being fed bystacker conveyors 19. Since boom arm 20 is not always horizontal, anygravity scale must be compensated for deviations from the horizontal togive accurate readings. For this reason, and others, applicant prefersto use a nuclear scale. Scales of this type are available commercially.One

scale that could be used is available from Ohmart, Inc. of Cincinnati,Ohio.

FIG. 7 shows the control system of the present invention. The nuclearscale 22 comprises sensing heads 32 and 33. Power is supplied by supply31 and the signal from sensing head 33- is amplified and linearized byamplifier 23. Sensing heads 32 and 33 are positioned so that thematerial on stacker conveyor 19 is measured. The output of scaleamplifier 23 is connected to one input of analog multiplier 24.Tachometer 30 is mechanically coupled to stacker conveyor 19 and sensesthe speed thereof. The tachometer 30 produces an electrical analogsignal proportional to the speed of the conveyor 19. This signalprovides the second input to analog multiplier 24. The output of analogmultiplier 24 is fed to potentiometer 25. Wiper 34 of potentiometer 25picks off a selected portion of the signal fed to the potentiometer bythe multiplier 24. The signal picked off by Wiper 34 is fed as one inputto the error amplifier 26. Tachometer 29 is mechanically coupled to oneof the stacker driving motors 28. This tachometer provides an outputsignal proportional to the speed of the stacker 11. The signal fromtachometer 29 provides the other input to error amplifier 26. Amplifier26 comprises the two input signals and the output is proportional to thedifference of these signals. The output of error amplifier 26 is fed tovariable frequency control 27. This converts the error signal into asuitable form for controlling the stacker drive motors 28. One suitableform of variable frequency control 28 is commercially available fromRamsey Controls, Inc., Mahwah, NJ. Although FIG. 7 illustrates only onemotorwheel combination, it should be understood that the stacker 11 isnormally provided with at least four or more driving wheels. Usuallyeach driving wheel is associated with a separate motor, so generallyfour motorwheel combinations will be present.

In operation, the stacker conveyor 19, operatively associated with thestacker trailer 9 delivers material to the bed. The material passesbetween sensing heads 3233- of the nuclear scale 22. The scale relies onthe reduction in transmission of radiation between sensors 32-33 toindicate the mass or weight of material. Power supply 31 and amplifierand linearizer 23- provide a signal proportional to the mass or weightof material on the belt. This signal may be quantized in terms of poundsper feet. Analog multiplier 24 multiplies this by the conveyor speedsignal from tachometer 30. The output of multiplier 24 is a signalproportional to mass flow which can be expressed as pounds per minute.The output from multiplier 24 is then applied to potentiometer 25. Thepotentiometer 25 is calibrated in terms of bed layer thickness as areciprocal function of its resistance. That is, maximum layer thicknesscorresponds to minimum resistance or the lower end of the potentiometeras shown in FIG. 7. With the wiper 34 at the midpoint, the result wouldbe a layer twice as thick as if the wiper were in the upper or position.

At any one setting of potentiometer 25, the control system operates asfollows. The nuclear scale output indicates the belt loading factor.Tachometer 30 indicates belt speed. The output of analog multiplier 24is proportional to mass flow which can be expressed in pounds perminute. The setting of potentiometer 25 corresponds to a preselectedlayer thickness. This selected portion of the output of multiplier 24 iscompared with a signal proportional to the speed of the stacker 11 asdeveloped by tachometer 29. The comparison is effected by erroramplifier '26 in a conventional manner. Variations in the amplitude ofeither or both inputs will vary the amplitude of the output of erroramplifier 26. In order to provide for direct motor control, thisamplitude signal is converted into a variable frequency signal byvariable frequency control 27. The output of variable frequency control27 consists of a signal whose frequency is related to the output oferror amplifier 26. This variable frequency signal is suitable tocontrol motors 28. This mode of operation will cause the stacker speedto compensate for changes in mass flow so as to maintain constant layerthickness. However, as explained above, it is sometimes desirable tovary layer thickness from one layer to the next. For instance, assume itis desired to provide a layer of /2 normal thickness. If normalthickness corresponds to the lower quarter point of the potentiometer,that is the 25% point, a layer of half this thickness can be provided byraising the potentiometer to the 50% point. In effect, this will doublethe voltage delivered by the potentiometer to the comparison circuit. Inorder to drive the error voltage to zero, which corresponds to theoutput of amplifier 26, the stacker speed will have to double. Withother factors being equal, this doubling of stacker speed will produce alayer which is /2 the thickness of the standard layer. Of course, ifeither of the other factors vary the control system will compensate forsuch variation by adjusting stacker speed to nullify the effect of anysuch unwanted variation.

Potentiometer 25 then presents the operator with a readilly controlledparameter which renders control of layer thickness a simple matter.Inasmuch as the only connections between the control system and theblending system itself are electrical, this is readily adaptable toremote operation. Automation can also be provided for simply. A programcan be written out in advance specifying which materials are to bedelivered on particular passes of the stacker. A counter would thencontrol the supply of material to conform to the program. If layerthickness were desired to vary, relays could be used to pick the properlayer thickness off of potentiometer 25 in response to the program andthe count stored in the counters. Such a system would completelyeliminate the operators.

The present system provides for remote operation of of the bed blendingsystem. With one setting, choosing predetermined layer thicknes, theoperator sets in motion the system. Variations in mass flow, which areunavoidable are automatically compensated for by the system by varyingthe stacker speed. The layer thickness then is unvarying longitudinallywhich is the sine qua non of the bed blending system. The control systemalso provides for readily variable layer thickness if necessary ordesirable when blending to a particular recipe.

I claim:

1. In a bed blending system including a conveyor system for feedingmaterial to a stacker,

said stacker feeding said material to a bed,

a control system for controlling the speed of said stacker comprising,

means to determine the rate of flow of material from the stacker,

means to measure the sped of said stacker traveling along said bed, and

means for comparing said speed with said rate of flow and control meansfor adjusting the speed of said stacker in accordance with saidcomparison.

2. The control system of claim 1 wherein said means to determine therate of flow of material from said stacker comprises a nuclear scalemounted on said stacker producing a first electrical signal proportionalto the mass of material passing a point on said stacker,

means for producing a second eletrical signal proportional to the speedof a conveyor on said stacker, and

multiplier means for multiplying said first two electrical signals toproduce a third electrical signal proportional to said rate of materialflow from said stacker.

3. The control system of claim 2 in which said means to measure saidstacker speed produces a fourth electrical signal proportional to saidstacker speed and where said means for comparing comprises a differenceamplifier which produces a signal proportional to the difference betweensaid third and fourth electrical signals.

4. In the control system of claim 3 which includes means to vary thethickness of the layer of material in the bed, said means comprises apotentiometer across which said third electrical signal is produced,said potentiometer being calibrated in terms of layer thickness, thewiper of said potentiometer feeding a selected portion of said thirdelectrical signal to said difference amplifier, the selected portionbeing in inverse proportion to said selected layer thickness.

References Cited UNITED STATES PATENTS 2,750,023 6/1956 Meissner 198--363,43 0,751 3 /1969 Bateson 19=8--39 3,441,039 4/1969 Rawson 239- GERALDM. FORLENZA, Primary Examiner J. MANNIX, Assistant Examiner US. Cl. X.R.19 8-486

